1. Field of the Invention
This invention relates to the field of integrated circuits and, more specifically, to a minimal corrosion resistor metallurgy and multi-focus deposition technique for applying closely overlapped mutually protective barrier films and resistive metal films to provide integrated resistors without incurring corrosion or interdiffusion failures.
2. Description of the Prior Art
Simple metal resistors of a metal such as titanium have many desirable features such as mechanical strength, thermal stability and easy control of resistance values, but are susceptible to corrosion when in contact with niobium films.
It is known in the field of integrated circuit fabrication that gold has desirable anti-corrosive barrier properties and that gold is a good conductor suitable for use as a metallization region. Certain gold alloys and gold layers have been used and suggested in a number of anti-corrosive contact characterizations. Gold, however, is not a good diffusion barrier.
It is known in the field of integrated circuit fabrication, particularly for cryogenic devices such as Josephson devices, that niobium is a useful superconductor, susceptible to passivation by oxidation, which is capable both in metallic form and oxide form of withstanding temperature cycling between room temperature .about.20.degree. K. and liquid helium temperature .about.4.2.degree. K.
Niobium is known to grow an intrinsic oxide, a surface layer of Nb.sub.2 O.sub.5 which forms naturally at ambient temperatures in ambient atmospheres containing oxygen.
For example, U.S. Pat. No. 4,310,569, Harrington, "Method of Adhesion of Passivation Layer to Gold Metallization Regions in a Semiconductor Device," Jan. 12, 1982, shows a gold-reactive metal interface, which interface provides improved adhesion for a subsequent passivation layer. Harrington does not, however, show any technique for passivating a ring around a barrier film to prevent corrosive intimate contact between incompatible materials.
U.S. Pat. No. 4,316,200, Ames et al, "Contact Technique for Electrical Circuitry," Feb. 16, 1982, shows the use of Nb.sub.2 O.sub.5 on the top and sides of a niobium metal layer to act as an electrical insulator, in the context of a cryogenic temperature integrated circuit. Ames et al does not, however, show any technique for passivating a ring around a barrier film to prevent corrosive intimate contact between incompatible materials.
U.S. Pat. No. 3,907,620, Abraham et al, "A Process of Forming Metallization Structures on Semiconductor Devices," shows a process for forming tantalum nitride layers on a semiconductor. Abraham et al does not, however, show any technique for passivating a ring around a barrier film to prevent corrosive intimate contact between incompatible materials. European patent 82101971.8, Gasser et al, shows a gold oxidation prevention film between the Josephson tunnel barrier (Nb.sub.2 O.sub.5) layer and an overlying niobium layer.
None of the prior art nor any combination of prior art teaches the close tolerance mutually protective corrosion barrier film/passivating ring/diffusion barrier resistive layer described in this patent specification, nor does the prior art in any way teach the method of using focus variations within an overhanging photoresist opening to provide close tolerance mutually protective corrosion barrier film/passivating ring/diffusion barrier resistive layer structure.